Polycrystalline silicon is a raw material used to produce many commercial products including, for example, integrated circuits and photovoltaic (i.e., solar) cells. Polycrystalline silicon is typically produced by a chemical vapor deposition mechanism in which silicon is deposited from a thermally decomposable silicon compound onto silicon seed particles in a fluidized bed reactor. These seed particles continuously grow in size until they exit the reactor as polycrystalline silicon particles product (i.e., “granular” polycrystalline silicon). Suitable decomposable silicon compounds include, for example, silane and halosilanes (e.g., trichlorosilane).
Polycrystalline seed particles may be added to the reaction chamber to initiate deposition of silicon. A variety of reactions may take place in the reaction chamber. Silicon deposits from silane onto a silicon particle, resulting in the particle growing in size. As the reaction progresses, silicon particles grow to a desired size and are removed from the reaction chamber and new seed particles are added to the reaction chamber.
Other processes conducted in fluidized bed reactors result in the reduction in size of particles within the reactors. For example, metallurgical-grade silicon and hydrochloric acid may be burned within the reaction chamber to produce trichlorosilane. During this process, the metallurgical-grade silicon particles are eroded and decrease in size as the reaction progresses. These particles are eventually removed once the particles have decreased to a certain size.
Various methods have been used to attempt to estimate the size of particles in the reaction chamber. In one method, the sample particles are removed from the reactor and allowed to cool, after which they are measured. But this method is incapable of real-time measurement of the particle size because there is considerable delay between removal of the particle from the reactor and determination of its size. Another method estimates the size of particles via stoichiometric methods. Still other methods attempt to estimate particle size based on the pressure of gas within the reaction chamber of the fluidized bed reactor. These methods have generally yielded unsatisfactory results.
This Background section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.